Peroxynitrite mediates calcium-dependent mitochondrial dysfunction and cell death via activation of calpains

Area of Science:

• Biochemistry
• Cell Biology
• Pathology

Background:

• Chondrocyte cell death is central to inflammatory and degenerative joint diseases like rheumatoid arthritis (RA) and osteoarthritis (OA).
• 3-nitrotyrosine, a marker for reactive nitrogen species (RNS) like peroxynitrite, is found in OA and RA cartilage and linked to chondrocyte death.
• The precise mechanisms of peroxynitrite-induced chondrocyte death remain unclear.

Purpose of the Study:

• To investigate how peroxynitrite induces cell death in human articular chondrocytes.
• To elucidate the molecular pathways and key mediators involved in peroxynitrite-induced chondrocyte apoptosis.

Main Methods:

• Human articular chondrocytes were treated with peroxynitrite or SIN-1 (peroxynitrite generator).
• Intracellular calcium levels, mitochondrial function, and cell viability (MTT assay, LDH release) were assessed.
• Apoptosis hallmarks (annexin V labeling, subG1 DNA content, DNA condensation) and caspase activity were evaluated.
• Caspase involvement was tested using Western blotting, fluorimetric assays, and caspase inhibition.

Main Results:

• Peroxynitrite rapidly increased intracellular calcium, causing mitochondrial dysfunction and cell death.
• Chondrocyte death displayed apoptotic features but lacked caspase involvement.
• Peroxynitrite did not inhibit cellular caspase activity.
• Cell death was predominantly mediated by calcium-dependent cysteine proteases (calpains).

Conclusions:

• Peroxynitrite induces mitochondrial dysfunction in chondrocytes through a calcium-dependent mechanism.
• This process leads to caspase-independent apoptosis mediated by calpains.
• Understanding this pathway offers new insights into joint disease pathogenesis and potential therapeutic targets.